Methods

Patients treated with SBRT from June 2008 to May 2010 at Georgetown University Hospital
for localized prostate carcinoma, with or without the use of androgen deprivation
therapy (ADT), were included in this retrospective review of data that was prospectively
collected in an institutional database. Treatment was delivered using the CyberKnife®
with doses of 35 Gy or 36.25 Gy in 5 fractions. Biochemical control was assessed using
the Phoenix definition. Toxicities were recorded and scored using the CTCAE v.3. Quality
of life was assessed before and after treatment using the Short Form-12 Health Survey
(SF-12), the American Urological Association Symptom Score (AUA) and Sexual Health
Inventory for Men (SHIM) questionnaires. Late urinary symptom flare was defined as
an AUA score ≥ 15 with an increase of ≥ 5 points above baseline six months after the
completion of SBRT.

Results

One hundred patients (37 low-, 55 intermediate- and 8 high-risk according to the D’Amico
classification) at a median age of 69 years (range, 48–90 years) received SBRT, with
11 patients receiving ADT. The median pre-treatment prostate-specific antigen (PSA)
was 6.2 ng/ml (range, 1.9-31.6 ng/ml) and the median follow-up was 2.3 years (range,
1.4-3.5 years). At 2 years, median PSA decreased to 0.49 ng/ml (range, 0.1-1.9 ng/ml).
Benign PSA bounce occurred in 31% of patients. There was one biochemical failure in
a high-risk patient, yielding a two-year actuarial biochemical relapse free survival
of 99%. The 2-year actuarial incidence rates of GI and GU toxicity ≥ grade 2 were
1% and 31%, respectively. A median baseline AUA symptom score of 8 significantly increased
to 11 at 1 month (p = 0.001), however returned to baseline at 3 months (p = 0.60). Twenty one percent of patients experienced a late transient urinary symptom
flare in the first two years following treatment. Of patients who were sexually potent
prior to treatment, 79% maintained potency at 2 years post-treatment.

Conclusions

SBRT for clinically localized prostate cancer was well tolerated, with an early biochemical
response similar to other radiation therapy treatments. Benign PSA bounces were common.
Late GI and GU toxicity rates were comparable to conventionally fractionated radiation
therapy and brachytherapy. Late urinary symptom flares were observed but the majority
resolved with conservative management. A high percentage of men who were potent prior
to treatment remained potent two years following treatment.